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RESOLVING THE FERMI PARADOX


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RESOLVING THE FERMI PARADOX

Rudy E. Kokich, Alexandra Kokich, Andrea Hudson

7 July 2018

 

 

 

 

Abstract:

 

In 1975 astronomer Michael Hart proposed the Fermi Paradox, implying a contradiction between the lack of direct evidence for extraterrestrial intelligence (ETI) and the presumed probability that they exist in substantial numbers. Recently, Oxford researchers Sandberg, Drexler, and Ord applied the Monte Carlo simulation to the Drake equation, and concluded that there is up to 99.6% probability that we are alone in the Milky Way galaxy, and up to 85% probability that no other intelligent life exists in the entire observable universe.

 

We submit that, from physical, chemical, biological, and statistical perspectives, these conclusions require Earth to occupy a singular environment in the universe which is estimated to contain one hundred billion trillion habitable exoplanets. Although there is no direct evidence for ETI, we propose that sufficient indirect evidence exists to reasonably hypothesize a profusion of simple extraterrestrial life and considerable numbers of intelligent life. We resolve the Fermi paradox by showing that the premise of the paradox represents a fallacy in informal logic, and that the paradox is a false dichotomy easily explained by insufficient investigation. By calculating the mean interstellar distance between presumed numbers of ETI in the galaxy, we show that, except by pure coincidence, the nearest ETI would lie hundreds or thousands of light years (LY) away. If highly advanced civilizations are also subject to the universal laws of nature, then traversing such distances, or even attempting radio communication, presents unrewarding if not insurmountable technological, social, and economic challenges. The impracticality of such enterprises is reinforced by the consideration that any possible proceeds would not arrive for scores of generations.

 

 

Fermi Paradox:

 

After a flurry of UFO sightings, during lunch with colleagues at Los Alamos National Laboratory in 1950, physicist Enrico Fermi estimated the probability of intelligent alien life in the galaxy, and raised the question, "Where are they?" If there are tens of billions of Sun-like stars with Earth-like planets, and some of them evolved intelligent life, why is there no record in human history of extraterrestrial visitors or their artifacts?

 

According to a Scientific American article by Robert H. Grey [1], Fermi's question was declared a "paradox" in 1975 by astronomer Michael Hart. He proposed that, if technological aliens existed, "they would inevitably colonize the Milky Way" either as individuals or with self-replicating robotic probes. The label Fermi Paradox, and the conclusion "... they are not here, therefore they do not exist," became accepted as popular wisdom, and were actually cited by Sen. William Proxmire in 1981 and Sen. Richard Bryan in 1993 to deny government funding for NASA's SETI program.

 

Written accounts of the 1950 Los Alamos lunch by physicists Emil Konopinski, Edward Teller, and Herbert York indicate that Fermi did not present his question as a paradox, and did not challenge possible existence of alien civilizations. According to York, Fermi "went on to conclude that the reason that we hadn’t been visited might be that interstellar flight is impossible, or, if it is possible, always judged to be not worth the effort, or technological civilization doesn’t last long enough for it to happen.”

 

Since 1992, nearly four thousand exoplanets have been detected, with 632 star systems having multiple planets. As our detection methods are mostly restricted to systems with planetary orbit planes in our line of sight, it is certain that we presently can not document a great majority of exoplanetary systems. Still, every year of research reveals the Solar System to be far from unique, and that most, if not virtually all, high metallicity Population I stars have planets, some of which are suitable for life. Nevertheless, the Fermi paradox, better renamed Hart Paradox, remains entrenched in popular and scientific thinking, asserting doubt in the existence of alien civilizations due to the absence of any positive evidence such as radio signals, extraterrestrial visitors, or robotic probes.

 

 

The Drake Equation and the SETI Model:

 

In 1961, several days prior to the first scientific meeting on the search for extraterrestrial intelligence (SETI), radio astronomer Frank Drake wrote an equation including seven variables which need to be considered when estimating the number, N, of civilizations in our galaxy capable of radio communication at the current time. [2]

 

N = R x Fp x Nc x Fl x Fi x Fc x L

 

R = rate of star formation in our galaxy.

Fp = fraction of those stars with planetary systems.

Nc = number of habitable zone planets per star system.

Fl = fraction of suitable planets on which life actually appears.

Fi = fraction of life bearing planets on which intelligent life emerges.

Fc = fraction of civilizations which develop suitable radio technology.

L = the length of time such civilizations release detectable signals.

 

During the original SETI meeting, attended among others by eminent astronomers Carl Sagan and Otto Struve, the seven parameters in the equation were largely based on conjecture. Educated guesses gave the minimum value for N as 20, and the maximum value of 50,000,000. The maximum value was skewed by the maximum estimate for L of 100 million years - assuming a geological scale for the lifetime of a technological civilization.

 

Since then, research has revealed much more precise estimates for the first three parameters in the equation. According to NASA and the European Space Agency, the rate of star formation in our galaxy ® is 1.5 - 3 stars per year, the fraction of stars with planetary systems (Fp) approaches 1, and the fraction of stars with planets in habitable zones (Nc) is roughly 0.2, or one in five. [3]

 

However, at the current stage of scientific development, there is no observational basis to assign values to the next three parameters. It is not known how often life develops on suitable planets, how often such life becomes "intelligent", or how often intelligent life develops technology. As for the lifetime of a technological civilization, it has been convincingly argued that it might last indefinitely if it overcame all threats to its survival, or that it might obliterate itself within several centuries or even decades.

 

Consequently, the Drake equation, written by Drake's own declaration as an agenda for a meeting, to stimulate scientific dialogue, can not be used to draw reliable conclusions regarding the number of technological civilizations in a galaxy. Depending on the assumed values for the unknown terms, the result may be from far less than one to tens of millions. Such a wide ranging approximation does not seem to be a useful scientific result as much as an estimate of the observer's pessimism or optimism.

 

 

The Oxford Model:

 

In a paper titled Dissolving Fermi Paradox, submitted to the Proceedings of the Royal Society of London, and published online at arXiv.org [4], three researchers at Oxford University's Future of Humanity Institute claim to have calculated significant probability that we are the only technological civilization in our galaxy, and even in the entire visible universe. The authors, Sandberg et al, treated each parameter in the Drake equation not as a single best guess point but as a series of uniformly selected values from a range of historically estimated uncertainty. Monte Carlo simulation [5] then yielded 53% - 99.6% probability that we are the only technological civilization in our galaxy, and 39% - 85% probability that we are alone in the observable universe. They declared the Fermi paradox dissolved since our failure to detect aliens is no longer in conflict with the expectation that they exist. In their own words, “we find a substantial ex ante probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it."

 

Although the authors approached the Drake equation with a more sophisticated statistical model, their results may be no closer to the unknown "reality" than the SETI Drake model. Their estimates of current scientific uncertainties, and therefore ranges assigned to the Drake parameters (in their Table 1), are highly debatable. Presenting the same results to show the probability that an extraterrestrial intelligence (ETI) does exist yields the lowest value for the the galaxy of

100% - 99.6% = 0.4%.

In a universe of 200 billion galaxies, the probability that ETI does exist would be:

1 - ( 0.004^2E11 ) = 1, or 100%, not 15%.

 

 

The Frank-Sullivan Model:

 

For yet another approach, consider the article A New Empirical Constraint on the Prevalence of Technological Species in the Universe [6] published by Frank and Sullivan in the journal Astrobiology. In order to remove unknown parameters from the Drake equation, Frank and Sullivan redefined the ETI question. "Rather than asking how many civilizations may exist now, we ask, are we the only technological species that has ever arisen?" Their equation becomes:

 

A = N x F        , where:

 

A is the number of technological species which emerged over the lifetime of the universe,

N is the number of habitable planets in the universe, and

F is the fraction of habitable planets on which technological species emerge.

 

Although simple, the equation can not be solved since parameters A and F remain highly speculative. The authors then redefined the question to find the probability against humanity being the only technological society which has ever developed in the universe. Parameter A now becomes 1, and the equation becomes:

 

F = 1 / N

 

The European Space Agency, estimates there are roughly 10^22 - 10^24 stars in the universe. [7]  According to the latest data from the Kepler space mission, approximately one in five stars has a planet in the habitable zone. Assuming the middle value of 5x10^23 for the number of stars in the universe, the number of habitable planets, N, is:

N = ( 5x10^23 ) / 5 = 1x10^23

and the probability, F, that humanity is the only technological civilization which has ever existed in the universe is:

F = 1 / ( 1x10^23 ) = 1x10^-23

or about one in one hundred billion trillion !

 

On the scale of our galaxy, assuming the number of stars to be 3x10^11 :

N = (3x10^11) / 5 = 6x10^10

F = 1 / ( 6x10^10 )

or about one in sixty billion !

 

However, these numbers are not as optimistic as they at first appear. Since the universe is 13.8 billion years old, if every single habitable planet in the galaxy eventually developed a technological civilization, that number would be 60 / 13.8 = 4.3, only about four per year. The estimated number of ET civilizations existent at the present time then strictly depends on the estimated longevity of a technological civilization - parameter L in the Drake equation. For supposed longevity of 1,000 years, the maximum number of contemporary galactic civilizations would be 4,300.

 

 

Validity of Statistical Models:

 

Various statistical models predict a wide range of outcomes: from no ETI in the entire universe to millions in our galaxy alone. Since all models depend on authors' assumptions and estimates rather than objective data, the fundamental question remains whether any statistical method can return valid information regarding an entity about which no factual knowledge exists. The only certitude, known from Earth's experience, is that a technological civilization is possible. The results obtained by the Oxford researchers may be only a reflection of the degree of their pessimism. In comparison, ETI probability evaluation made at the first SETI meeting, although equally uncertain, seems to have been drawn by a highly optimistic group. Whether we accept a universe in which we are absolutely alone, or one which is teeming with intelligent life depends at this time entirely on our subjective intuition of what is "reasonable". And, what is reasonable depends to a major degree on the three unknown parameters in the Drake equation: Fl, Fi, and Fc.

 

 

Estimates of Three Drake Parameters:

 

Knowing only Earth's example, we have no information to define Fl, the fraction of suitable planets on which life actually appears. On Earth, the earliest evidence of life in the form of fossilized microorganisms was found in Canadian sedimentary rocks, interpreted as submarine hydrothermal vent precipitates, and dated between 3.77 and 4.28 billion years old. [8]  In another study, UCLA geochemist Mark Harrison found carbon isotope evidence of life in 4.1 billion year old zircon crystals from western Australia. These studies extend by up to 300 million years the generally accepted age of Earth's oceans (3.8 billion years) which are thought to be necessary for the emergence of life.

 

Numerous planetary missions have revealed that geological features like volcanoes, mountains, lake beds, sea basins, river deltas, sedimentary rocks, and erosion due to wind and heavy rainfall are present on other planets. We are now developing instruments capable of detecting in the atmospheres of  exoplanets indirect evidence of alien life like methane, oxygen, and complex organic molecules. In fact, such molecules have only recently been reported in the plumes emerging from Saturn's moon Enceladus, suggesting the possibility of a deep-ocean thermal vent biosphere.

 

As years go by, it is ever more apparent that there is nothing unique about our Sun, the Solar System, or the Earth itself. There seems to be nothing exclusive about our geology, chemistry, or physics. Since the laws of nature observed on Earth are equally valid elsewhere in the universe, it seems irrational to cast heavy doubt on the possibility that organic chemistry on suitable exoplanets will evolve into primitive life. The evidence that life appeared only several hundred million years after Earth's formation 4.54 billion years ago might imply that life is plentiful throughout the universe, and dispose us to assign higher values to parameter Fl - perhaps close to 1.

 

Estimating parameter Fi, the fraction of life-bearing planets on which intelligent life emerges, is more difficult. If the passage of time between two related events reflects the probability of the second event, then on Earth it took about 3.5 billion years for early life to develop primordial intelligence in the form of fish. This process took nearly a quarter of the age of the universe, and involved a number of complex stages:

1) the emergence, by prokaryotic endosymbiosis, of eukaryotic cells with a nucleus and membrane-bound organelles, about 2 billion years ago [9];

2) the emergence of **** reproduction about 1.1 billion years ago;

3) the appearance of multicellular animals in the fossil record about 600 million years ago [10]; and

4) the appearance of an elementary brain in bilaterally symmetrical animals, roughly 550 million years ago. [11]

 

Another 350 million years passed before the mammals, the first class of animals we would consider conventionally "intelligent", developed the cerebrum, or neocortex, which is associated with higher cognitive functions. [12]

 

In the Earth's example, the long time frame involved in the emergence of intelligence implies a low value for parameter Fi  but, in the absence of many additional samples, does not suggest any specific quantity.

 

Before evaluating a "reasonable" estimate for parameter Fc, the fraction of planets on which intelligent species develop technological civilizations, we need to consider issues related to human self-perception.

 

In part due to human nature, and in part to incomplete observational evidence, throughout history mankind has always made the initial assumption that it is unique, and occupies a special place in creation. Since the beginning of time this tendency heavily influenced our political history, socioeconomic development, and science - especially cosmology and biology.

 

Initially we believed in the Ptolemaic geocentric system, in which Earth occupied the center of the universe. Science gradually demoted us to a small planet around a random star, in an ordinary galaxy, arbitrarily located among several hundred billion in the visible universe, which itself may be only an insignificant fraction of an infinite multiverse.

 

In the field of biology, mankind also made the initial assumption that it is unique. Until recently scientists were trained to strictly guard against anthropomorphism. Man was presumed to act by reason and independent thought, and animals only by instinct. However, latest research by behavioral and neuro-scientists reveals that higher animals also perceive physical sensations and a spectrum of emotions just like we do. They observe, think, learn, communicate, use tools, form societies, and modify their behavior in a logical manner consistent with self-interest. Human distinction appears to be a matter of degree rather than the kind of ability. If we abandon the perspective that we are biologically unique, we can observe that on Earth only about two hundred million years - a blink of the cosmological eye - separate the first animals with a complex brain from the first technological civilization.

 

This implies a rather high value for Drake parameter Fc, perhaps also approaching 1.

 

The most time consuming, and presumably least probable, stages in the evolution of life on Earth were the emergence of eukaryotic cells and the emergence of multicellular animals. Avoiding the temptation of excessive self-regard, and using Earth as a model for other habitable planets, probabilities favor a galaxy teeming with primitive life, but with low incidence of even elementary intelligence. Yet, where primitive brains do develop, complex brains evolve in 350 milion years, and a technological civilization follows in about 200 million.

 

An interesting proposition was put forth at the first SETI meeting: that with some Drake parameters high, like R, and some low, like Fi, the product of the first six parameters is very approximately equal to 1, and the number of contemporary technological civilizations in our galaxy, N, is numerically equivalent to L, the number of years such civilizations persist. Considering the Earth model, this proposition is not entirely unreasonable - within an order of magnitude. Since Homo sapiens emerged about 300,000 years ago [13], with this approach the number of alien species of approximately human intelligence might be tens or even hundreds of thousands in the galaxy.

 

However, that does not answer Drake's question. He specifically asks how many technological civilizations are detectable. Of the ones which have the ability, how many are actually beaming powerful radio signals precisely in our direction, over very long periods of time, attempting a contact? That number is likely to be far, far lower.

 

Clearly, estimated numbers of alien civilizations will vary widely based on the initial conditions imposed by very specific questions. What is intelligence? What is technology? What is detectable? Do aliens have to be biological, or can they be composed of semiconductors, in which case their longevity as individuals and as a species might be much greater?

 

 

Challenging the Fermi Paradox:

 

In an article An Explanation for the Absence of Extraterrestrials on Earth published in the Quarterly Journal of the Royal Astronomical Society in 1975, astronomer Michael Hart wrote: "We observe that no intelligent beings from outer space are now present on Earth. It is suggested that this fact can best be explained by the hypothesis that there are no other advanced civilizations in our galaxy." [14]  This concept, labeled Fermi paradox, was predicated on the assumption that technological aliens, if any ever existed, would have inevitably colonized the entire galaxy over millions of years. 

 

The so called Fermi paradox has been challenged on many levels [15], most of which are reasonable and a few conspiratorial. But one obvious question has to come first. Is Michael Hart's statement logical?

 

The first part of Hart's contention: "ETI are not observed, therefore ETI are not here" is false because it requires omniscience on the part of the observer. ETI might very well be here and not observed because the observer has limited perceptions. The second part: "ETI are not here, therefore ETI do not exist" is also false because the premise (ETI are not here) may be false, and because ETI may very well exist in many places, but not specifically here. If Hart's contention is false, the paradox does not exist.

 

As the ancient Romans originally reasoned, absence of evidence does not imply evidence of absence. No valid conclusion can be inferred from the absence of evidence because evidence may be lacking due to insufficient investigation. Indeed, we have not yet made a detailed investigation of our own solar system, much less of the galaxy or the universe.

 

Logical error in Hart's Fermi paradox implies an invalid approach in using that line of reasoning to explain lack of contact with the aliens, or to estimate the probability of their existence.

 

 

Is Earth Unique in the Universe?:

 

At this stage of our scientific knowledge any discussion of intelligent aliens, or even of alien life, constitutes pure speculation. This does not mean the speculation is mere guesswork. We do have some indirect information on which to base an educated opinion. With relatively high confidence, we know the following:

-Life developed very early in the history of our planet.

-The probability of life increases in proportion to the number of suitable environments.

-Life is highly adaptable to extreme environments and to competition.

-Probability of complex organisms increases with the passage of time.

-Evolutionary pressures favor the emergence of the brain and intelligence.

-Some intelligent species can develop technology.

-We have observed that natural laws appear to be universal.

-We presently know that most, if not all, stars have planetary systems, and that approximately one in five have planets in the habitable zone. There are likely tens of billions of suitable planets in the galaxy, and billions of trillions in the universe.

-Although we are unique as spiritual individuals, there is nothing exclusive in our collective physical existence as a species.

 

Assuming Earth is not singular, but a random sample of habitable environments in the universe, an educated argument in favor of intelligent aliens vastly outweighs any argument against their existence.

 

 

How Far are the Aliens?:

 

Mean interparticle distance equations can approximate mean distance between star systems potentially populated with extraterrestrial intelligence. In a three dimensional space model, where V is the volume of a cube with a specified side S, and N the number of ETI contained in that volume, mean distance between ETI, D, is given by:

 

D = ( V / N )^1/3      where V = S^3

 

However, the galaxy is roughly 100,000 LY in diameter, and on average only 1,000 LY in thickness. The largest three dimensional cube which can be drawn within the galaxy would have a side of 1,000 LY, and a volume V = 10^9 cubic LY. Since the approximate volume of the Milky Way is 8x10^12 cubic LY, the galaxy can be divided into 8,000 such 1,000 LY cubes. On the small scale, where the mean distance between ETI stars is less than about 1,000 LY, sections of the galaxy are most accurately modelled in three dimensions.

 

On the large scale, the galaxy as a whole has the appearance of a flat pancake, and is best modelled in two dimensions as an area, A, of a circle with a radius R = 50,000 LY. The equation then becomes:

D = ( A / N )^1/2      where A = p x R^2

 

As the chart below shows, which scale, or volume model, is used depends on the total proposed number of ETI in the galaxy. When the number reaches 8,000 the mean distance between ETI is 1,000 LY, and the volume model can be shifted to three dimensions.

 

 

 

 

Illustration 1: Mean distance between ETI based on the proposed ETI number in the galaxy.

 

 

The results are shown in the semi-log graphical form in illustrations 2 and 3 below.

 

Illustration 2: Mean distance between ETI using the 2D model of the entire galaxy.

 

Illustration 3: Mean distance between ETI using the 3D 1,000 LY cube model.

 

The results are quite sobering. If there were 10 alien civilizations in the galaxy, the mean distance between them would be 28,025 LY. If there were 16,000, the distance would be 794 LY. As the 3D model shows, there would have to be 80 million ETI in the galaxy before we could expect to have a "local neighbor" within about 50 LY. Even by the most optimistic estimates the likelihood is that the nearest ETI lie hundreds, if not thousands, of light years away. This is reason enough to understand why the probability of any type of contact is vanishingly small.

 

 

Impediments to Contact:

 

Physical contact would involve traversing at relativistic velocities unimaginably vast distances through interstellar space filled with high energy plasma, strong cosmic radiation, dust, meteoroid material, and even undetectable black holes, rogue planets and comets. With our current technology and scientific knowledge we can not even hypothesize how - or even why - such voyages might be undertaken by biological or artificial species. In practical terms, millenia upon millenia would pass before any rewarding information could return to the home planet.

 

It is true that presently, at the very dawn of the space age, our theoretical and technical abilities are expanding at an exponential rate. But, at some point science will encounter the law of diminishing returns, and the learning curve will become sigmoid. We should not expect that anything we can now imagine will eventually become possible through science and technology. It is likely that even the most advanced civilizations are not able to violate the basic laws of nature by travelling faster than light, traversing space through "wormholes", moving backward in time, or altering the gravitational constant. In that case, alien space travellers are as constrained as we are by the laws of physics and biology, and by the economies of time and resources.

 

At present, the most promising method of detecting ETI is by searching for their radio signals. We have been transmitting broad-band, omnidirectional radio broadcasts for about a hundred years. In theory, our signals have already reached about 500 local stars. However such signals are probably not detectable beyond a fraction of a light year due to rapid dissipation and strong cosmic interference. Historically, SETI scientists have been searching for very narrow-band signals in the microwave region of the electromagnetic spectrum between 1 and 9 GHz. This region has relatively little background cosmic noise, and contains two narrow emission lines, including hydrogen at 1.420 GHz and methanol at 6.667 GHz, which are felt to be universal "radio dial markers". So far, SETI research has been unsuccessful. Even a narrow-band signal is not detectable at great distances unless it is emitted by a very powerful transmitter, and directed in a tight beam precisely in our direction. Then, the signal has to last long enough to be accidentally detected by SETI's narrow, star by star search. [16]

 

Even an optimist recognizes very low probability of detecting a powerful beacon aimed specifically in Earth's direction by an ETI which is eager to eternally advertise its presence at substantial economic cost, with indeterminable risk, and with extremely low probability of a reply delayed by many generations.

 

 

Conclusions:

 

In the end, the Fermi paradox as defined by Hart, which infers that ETI do not exist because we have no evidence of them, is a fallacy in informal logic because it relies on obviously insufficient investigation to promote its conclusion. Yet, the question, originally asked by Fermi himself, of why there is no record in human history of extraterrestrial visitors or their artifacts, is quite valid, and central to the formulation of hypotheses for further research.

 

Over the years, numerous answers to Fermi's question have been offered in scientific and popular literature. Some of them are rational, and others outlandish. The most plausable answer, already proposed by Fermi, seems to be the most obvious. Interstellar travel at relativistic speeds over distances of hundreds or thousands of light years is technically not practical, economically unproductive in terms of expense / reward ratios, and socially unintersting since required time frames call for scores of lifetimes of biological and even artificial life forms. Under these constraints, radio contacts are also unlikely because that would involve sustaining complex, expensive projects over thousands of years, with very unpromising prospects.

 

It may be suggested that scientific progress in more advanced civilizations might eventually solve some of the problems which to us presently seem theoretically insurmountable. That may not be the case. The growth of scientific knowledge can not forever accelerate at an exponential rate. It will eventually encounter the law of diminishing returns, slow down, and gradually approach some upper limit - hopefully in a very distant future. Technological capabilities of very advanced ETI might be far ahead of ours, and appear "miraculous", but are not likely to be infinite. Advanced aliens' knowledge of physics would probably refine but not invalidate our modern physics, just as Einstein's refined but did not invalidate Newton's. We should therefore not expect advanced aliens to possess technology which allows them to violate the fundamental laws of nature as we understand them today. In essence, like us, they will be subject to the same basic constraints of speed, space, time, and fundamental physical constants. This is the simplest explanation for why we have not had any proven alien contacts.

 

The existence of ETI does not depend on our knowledge or ignorance of them. They either emerged or did not emerge. Statistical models attempting to estimate the number of ETI based on indirect evidence implied in the Drake parameters produce results ranging from millions of ETI in the galaxy to none in the entire universe. Alhough it is impossible to quantify how these models reflect reality, the Oxford model which estimates high probability that we are alone in the visible universe implies a related conclusion: that Earth is somehow unique among the estimated one hundred billion trillion habitable exoplanets. On other suitable planets either life never arises, or it does not evolve into more complex forms, or it never develops intelligence, or intelligence never matures into science and technology. Making such an extraordinary claim carries the burden of extraordinary proof, far beyond numerical outcomes of a statistical model.

 

In fact, astronomers are commonly making discoveries that, compared to other stars in the galaxy, the Solar System and Earth are not exceptional in the physical or chemical sense. Rather than a singular case, it is almost infinitely more likely that Earth represents a random sample of habitable planets, and that processes observed here are common elsewhere in the universe. It follows that it is most reasonable to propose the hypothesis that on habitable exoplanets simple life exists in profusion, and intelligent life in unknown but "substantial" numbers.

 

And, what of the average lifespan of a technological civilization? Extinction rates from the fossil record suggest that the average lifespan of an invertebrate species is around 11 million years, while a mammal species lasts about 1 million years. [17]  In addition to the dangers from the natural biological, environmental, geologic, and cosmic catastrophies, the survival of a technological society is threatened by the capacity for self destruction. But while science and technology can be an existential threat, they also allow for self-preservation. Improvements in agriculture, medicine, and socioeconomic condition have allowed the human race to become the dominant species on Earth. Further benefits to survivability may lie in  diversification by constructive bioengineering, development of artificially intelligent life forms, and colonization throughout home-star systems. Such enterprises would disperse risk, enable a species, or its various versions, to achieve great longevity, and significantly increase the total number of contemporary ETI.

 

Finally, the answer to Fermi's question is different for the optimists and the pessimists.

 

Fermi already provided answers for the optimists. The galaxy may indeed be teeming with intelligent aliens but, in Herbert York's words, Fermi thought that "...interstellar flight is impossible, or, if it is possible, always judged to be not worth the effort, or technological civilization doesn’t last long enough for it to happen.”

 

For the pessimists who claim we might be the only technological civilization in the galaxy and even in the universe, in strictly scientific terms we must admit ignorance in view of complete absence of direct evidence. But, we also have to qualify that ignorance. Due to the vastness of the universe and the relative modesty of our instruments, our investigations have been astonishingly limited. To paraphrase astrophysicist Neil deGrasse Tyson, we have dipped a glass into the ocean, looked into it, and declared, "There are no whales."

 

 

 

References:

 

[1]      https://blogs.scientificamerican.com/guest-blog/the-fermi-paradox-is-not-fermi-s-and-it-is-not-a-paradox/
 
[2]      https://www.seti.org/drake-equation

https://exoplanets.nasa.gov/news/1350/are-we-alone-in-the-universe-revisiting-the-drake-equation/

https://en.wikipedia.org/wiki/Drake_equation
 
[3]      https://exoplanets.nasa.gov/news/1350/are-we-alone-in-the-universe-revisiting-the-drake-equation/

https://en.wikipedia.org/wiki/Drake_equation
 
[4]      https://arxiv.org/pdf/1806.02404.pdf
 
[5]      https://en.wikipedia.org/wiki/Monte_Carlo_method
 
[6]      https://www.liebertpub.com/doi/pdfplus/10.1089/ast.2015.1418
 
[7]      https://www.esa.int/Our_Activities/Space_Science/Herschel/How_many_stars_are_there_in_the_Universe
 
[8]      https://www.nature.com/articles/nature21377
 
[9]      https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_03
 
[10]      https://astrobiology.nasa.gov/news/how-did-multicellular-life-evolve/

http://science.sciencemag.org/content/346/6208/426
 
[11]      https://en.wikipedia.org/wiki/Evolution_of_nervous_systems
 
[12]      https://en.wikipedia.org/wiki/Evolution_of_the_brain
 
[13]      http://humanorigins.si.edu/evidence/human-fossils/species/homo-sapiens
 
[14]      http://adsabs.harvard.edu/full/1975QJRAS..16..128H
 
[15]      https://en.wikipedia.org/wiki/Fermi_paradox

https://www.space.com/37157-possible-reasons-we-havent-found-aliens.html
 
[16]      http://www.setileague.org/articles/sensitiv.htm

https://www.seti.org/faq#seti4
 
[17]      https://en.wikipedia.org/wiki/Background_extinction_rate
 

 

 


  • Inkswitch, llanitedave, elwaine and 6 others like this


125 Comments

When I was a student one of the big unknown variables was the number of stars with planets, and the number of those in the habitable zone.  Oddsmakers at the time thought exoplanets would range between rare and almost non-existent, with fewer still in the very narrow habitable zones.

 

Now we know that practically every star has a planetary system, and that almost any planet or moon can be habitable, even in the icy outer reaches of the system.

 

Extrapolation from a single data point is too mind bending for me.

    • ShaulaB, rowdy388 and CockatooDude like this

Also consistent with the Fermi paradox is that we are too primitive to notice anything and too commonplace to be studied intrusively.

    • siriusandthepup, pkrallis, Astrojensen and 3 others like this

I doubt if we could even define intelligent life and I agree with Araguaia that the probability

is that life is everywhere. My idea of intelligence is the ability to solve problems. That would

indeed be a competitive advantage. Too much intelligence could also be a two edged sword

leading to one's eventual destruction as a species. I think the jury is still out on that one.

Take me to your leader.   But really, not convinced either way.  Regarding the article,  the very notion that they could colonize was as far as I needed to go.   We should not use one unresolved question to argue another.  jd

If ETI exists, I'll be afraid.

If ETI doesn't exist, I'll be very afraid.

    • Procyon and rekokich like this

I thought that was a well articulated article. Part of the problem I've had with the Fermi paradox is that it assumes a galactic-hopping civilization would want to land on Earth in the first place. Well, if they didn't find our planet habitable to their needs, or the resources they expected to find on our planet wouldn't help them in any foreseeable goal, why would they trudge thousands of light-years in this direction just to say they did? At that point they would have landed on thousands or millions of other planets, if Earth showed no promise they wouldn't have wasted their time. So, the Fermi paradox states "we should have seen them already!" but no, perhaps our planet just wasn't interesting enough to waste time landing on in the first place. 

    • llanitedave, S1mas, PhilEdmonds and 1 other like this

We say intelligent but we're basically using that as shorthand for intelligences that we can communicate with, i.e. human-like enough.

 

We have four types of creatures on Earth that demonstrate intelligence: primates, cetaceans, cephalopods, and certain parrots. If we could effectively communicate with them, I'll believe we're capable of communicating with a hypothetical ET. 

 

There's no purpose to evolution, and there's nothing that says intelligence has to resemble human intelligence. 

 

There could be fearsomely intelligent creatures out there who have zero interest in communicating with others.  There could be others that are violently xenophobic. There could be others that communicate with chemicals on their skin and have no human analog. There could be others that have no mathematics like ours.

 

Endless possibilities. 

    • S1mas, rowdy388, Lola Bruce and 1 other like this

We assume intelligence is the highest form of creatures in the universe. There may be 1000s of creatures passing by looking at the Earth saying, "no need to stop, they are just a bunch of intelligence creatures down there. They got a long way to go before they become relevant."

 

Also this happy zone of life we live in is only a happy zone for us. The creatures living on Pluto would hate it here with all this heat and liquid water. To them this planet could never support any form of life. Just the mere suggestion of this Earth planet supporting life would be laughable, at most it could only support very primitive biological life no higher then having the simplest form of intelligence that couldn't do anything more then building some minor machines like rockets or computers. (Plutotonian's laughter can be heard)

 

We think like earthlings, time to think beyond that.

    • S1mas likes this

Great write up! Loved all the background history on the subject(s). 

My personal opinion, and its an opinion not any scientific fact, is that the odds of INTELLIGENT life in our own galaxy is extremely small.  The odds of everything coming together from the start of a star forming, to a planet forming in the perfect position around a perfect star, to life forming on said perfect planet, to life surviving long enough to form any level of intelligence, then that intelligent life creating technology needed for contact is just too many very specific ducks in a row to have anything but very lows odds of happening. Let alone multiple and multiple of times in one galaxy multiplied by the 200B+ galaxies. I just think logically the cosmological odds are just too small. Then again I see no whales in my glass lol. 

I do disagree that we are the only intelligent life in the universe though. Is just too vast with too many variables to rule out. My, very unscientific guess, is there probably averages 1 intelligent life in every galaxy, maybe more, but the odds just are not in that favor. 

I want to make clear I'm talking about intelligent life not just life in the general definition of the word. 

Again, great write up OP. I appreciated the read.

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siriusandthepup
Sep 11 2018 01:12 AM

We are going to find that life is the rule in the universe, not the exception.

 

This will happen in this solar system first.

-Life developed very early in the history of our planet.

Yes, but that was not early on in the history of the universe. Makes sense that we need stars and so planets that are of similar age. No carbon or other elements in the first stars or universe.

 

-The probability of life increases in proportion to the number of suitable environments.

Pretty obvious really.

 

-Life is highly adaptable to extreme environments and to competition.

Is it? Also if it fighting for existance can it develop further.

 

-Probability of complex organisms increases with the passage of time.

Seems reasonable. Also however destruction of complex life increases with time. Mars perhaps is an example.

 

-Evolutionary pressures favor the emergence of the brain and intelligence.

Cannot see a reason for this assumption. How long were dinosaur's around. Have seen it stated "Intelligence is not a prerequisite for life." At least not great intelligence. Consider the US tar pits from which many bones and skeletons are found. If intelligent after the number of years they existed wouldn't the creatures have avoided them? Put a sign up "Danger Tar Pit".

 

-Some intelligent species can develop technology.

Again yes, but not all, however you need the intelligence first.

 

Problem I have is that everyone argues their side, either for or against. Drake equation is too simplistic, and the people at the meeting/conference were all and only people that wanted to find other life. In effect the conclusion was set before it even started.

-Life is highly adaptable to extreme environments and to competition.

Is it? Also if it fighting for existance can it develop further.

 

-Evolutionary pressures favor the emergence of the brain and intelligence.

Cannot see a reason for this assumption. How long were dinosaur's around.

1) Evolution is fastest when selective pressure is highest.

 

2) Dinosaurs were more intelligent than fish.  Fish are more intelligent than marine worms.  The trend towards complexity and intelligence is clear.

    • North of Sixty likes this

The colonization, or "infection", model, does a pretty good job of colonizing the galaxy on time scales on the order of galactic rotation, which you can also think of as a mixing rate. But it does mean that the time SINCE colonization is on the same order of magnitude, i.e. a few hundred million years. But if you have efficient colonizers, even if they are slow, they will get the job done eventually. At least that's my impression from some low-fidelity modeling. There should be solutions where you can have many civilizations popping up, colonizing, and dying out within the galaxy with non-relativistic travel speeds (still requiring immense amounts of energy, that is another pacing parameter I think). If you've ever played the old Conway's "game of life" (a computer sim game from the 1970s) you know what I mean. So the probability of being contacted NOW is tiny, but the probability of having been contacted (colonized) in the geological past is not tiny.

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llanitedave
Sep 12 2018 12:22 AM

I thought that was a well articulated article. Part of the problem I've had with the Fermi paradox is that it assumes a galactic-hopping civilization would want to land on Earth in the first place. Well, if they didn't find our planet habitable to their needs, or the resources they expected to find on our planet wouldn't help them in any foreseeable goal, why would they trudge thousands of light-years in this direction just to say they did? At that point they would have landed on thousands or millions of other planets, if Earth showed no promise they wouldn't have wasted their time. So, the Fermi paradox states "we should have seen them already!" but no, perhaps our planet just wasn't interesting enough to waste time landing on in the first place. 

This was an extremely well-done article.  I enjoyed reading and musing about the possibilities, and the analysis was well thought out.

 

To build on RyanSem's idea, it's interesting to consider it might not be just the Earth that would be considered inadequate for a space-faring civilization (Including, maybe, future humanity).  As Tsiolkovsky famously said, "Earth is the cradle of mankind, but one cannot remain in the cradle forever."  That is just as true for any other advanced civilization developing on another planet.  When we look at the place to find abundant and easily retrievable resources beyond Earth, we're not really gaining anything if we simply look for another copy of home.  For a technological species with the capability to travel throughout its solar system and beyond, the most practical sources of raw materials and energy are to be found in the small icy bodies of the Oort clouds.  I would suggest that, if we suspect there are such advanced technologies, that's where we should concentrate our search.

 

In the Drake Equation, there's a heck of a lot of distance between Fl, Fi, and Fc.  It would be interesting to insert some "Rare Earth" hypothesizing into the mix.  One way that the Earth is a "Goldilocks Planet", and possibly an unusual feature compared to other Earthlike planets, is that it contains a "just right" volume of water.  Not only do the oceans make up 70% of the Earth's surface water, but much of its upper crust is saturated, and it turns out there is even more water in the mantle.  If Earth had accumulated just a little bit more during its formation, it would now be a water planet with little or no exposed land surface.  In such an environment, life might develop easily, and possibly even evolve substantial intelligence, but it's difficult to imagine them harnessing fire, mastering metallurgy, and developing a space-faring technology.

 

On the other hand, just a little less water, and seas would be small, and maybe ephemeral.  The vast deserts would be hostile to most life, evolutionary histories would be localized and truncated, and it might be much harder to develop the complexity required for advanced behaviors.  These conditions might conspire to make Earth-type life, and the ability to envision crossing the galaxy, a rare commodity indeed.

 

Of course, they might not!

 

We can take comfort in one thing, though.  In a 10" telescope, a solar-brightness star can be visible to a bit more than 3,000 light years.  In a 16" telescope, the visibility is twice that.  So if there is a better than vanishingly small chance of civilizations developing in our galaxy, it's quite possible that we can go out on any given night and sweep our eyes across one!

    • russell23 and S1mas like this

All these colonization models assume that altering planets to suit your biology is as easy or easier than interstellar travel.

 

And yet in our own example, we are close to send the first probes to Alpha Centauri, but have no idea how to stop wrecking our still-functioning biosphere.  But people in the space business throw around idle talk of terraforming Mars.

    • S1mas likes this

This was an extremely well-done article.  I enjoyed reading and musing about the possibilities, and the analysis was well thought out.

 

To build on RyanSem's idea, it's interesting to consider it might not be just the Earth that would be considered inadequate for a space-faring civilization (Including, maybe, future humanity).  As Tsiolkovsky famously said, "Earth is the cradle of mankind, but one cannot remain in the cradle forever."  That is just as true for any other advanced civilization developing on another planet.  When we look at the place to find abundant and easily retrievable resources beyond Earth, we're not really gaining anything if we simply look for another copy of home.  For a technological species with the capability to travel throughout its solar system and beyond, the most practical sources of raw materials and energy are to be found in the small icy bodies of the Oort clouds.  I would suggest that, if we suspect there are such advanced technologies, that's where we should concentrate our search.

Agreed. We also have to take into consideration the reason for expanding in the first place - likely to bring a better life for whichever civilization is expanding. If other intelligent species are bound by the laws of physics (spoiler, they are) then they're not going to reach a new planet any quicker than we would be able to. This means a necessary multi-generation-long flight just to arrive at the new planet before harvesting some resources to bring back. 

 

Unless there are self-replicating robots doing this work, or the people aboard these ships are enslaved in some way, I can't imagine a species willing to go on a 400 year journey to Earth just for the mediocre amount of rare resources we contain compared to other planets. Estimates I've seen to get to our closest star, Alpha Centuri, is 200 years with an antimatter drive (of course this technology isn't even fathomable right now). This would necessitate having and raising children in space no fewer than 7-8 times in just one direction (assuming a similar reproduction cycle and life span to humans). All these generations later they're supposed to stay on target and bring stuff home? My point is, if true space exploration is an act out of bettering the species' own lives, why would anyone agree to "waste" generations of their future family on traveling to a planet without much promise? 

 

To make matters more difficult, should they come close enough and catch our radio signals, we would be encountering a species who have lived their entire lives in a spaceship (and their great-great-great-great grandparents did too). Would they get spooked and abort the mission? There's no reason to believe they've ever negotiated inter-species relationships before, and any example of it in their civilization's history was just a lesson aboard a spaceship years ago. Unless a galactic fleet was descending on our solar system (requiring that many more families to agree to waste 400 years of family progeny) they'd be ill equipped to do anything except hope we won't blow them to smithereens. At that point maybe it's a matter of "they're more scared of you then you are of them".

 

Now, there are a slew of arguments against what I just said, I just thought it was an interesting exercise in the theoretical.  

    • llanitedave, City Kid, rekokich and 2 others like this

You can get to Alpha Centauri in 40 years using a laser sail.  The basic technology is well understood and has been tested on a tiny scale.  The only major challenge is to scale it up.

 

OTOH, altering the biosphere of a planet so that its gas mix, climate, etc. become inhabitable for an alien species is something that takes nature tens or hundreds of millions of years (see: the oxygenation of the Earth by cyanobacteria).  And we are very, very far from understanding what it takes, let alone to be able to do it artificially, in a controlled manner, and thousands of times faster. 

 

The generations that would have to be born and die in wait for an interstellar mission are nothing compared to how many would have to pass before you could take your spacesuit off on another planet.  Look at our political systems: they can't plan anything beyond ten years.  That is why no one went to Mars.  You really think a social species can organize and follow through with hugely expensive projects that will yield no benefits at all for several millenia?

    • llanitedave likes this

You can get to Alpha Centauri in 40 years using a laser sail.  The basic technology is well understood and has been tested on a tiny scale.  The only major challenge is to scale it up.

 

OTOH, altering the biosphere of a planet so that its gas mix, climate, etc. become inhabitable for an alien species is something that takes nature tens or hundreds of millions of years (see: the oxygenation of the Earth by cyanobacteria).  And we are very, very far from understanding what it takes, let alone to be able to do it artificially, in a controlled manner, and thousands of times faster. 

 

The generations that would have to be born and die in wait for an interstellar mission are nothing compared to how many would have to pass before you could take your spacesuit off on another planet.  Look at our political systems: they can't plan anything beyond ten years.  That is why no one went to Mars.  You really think a social species can organize and follow through with hugely expensive projects that will yield no benefits at all for several millenia?

Interesting on the solar sail. The rest of your post is definitely accurate about environmental conditions. I always figured they would use planets unsuitable to life for resources though, not secondary habitations, so the waiting period isn't needed if they're just beaming down to collect some loot before moving on. 

 

To your last point, I'm inclined to agree but we're assuming similar personalities of the ETI to those of humans in that case. Maybe they're all really cooperative! wink.gif

    • llanitedave likes this

If all they want is resources they will stick to the smaller gravity wells in the outer reaches of star systems.  More volatiles too, farther from the heat central star.

 

It doesn't matter if they are cooperative.  The problem is the discount rate and risk management.  If all goes well you still get no return on your investment for thousands of years.  If not, you lose everything - and there are a thousand ways the project can go wrong.  Odds are that it will, with the long time available for small deviations to accumulate.   Terrible investment.

Wow, that was a great read! Makes you feel glad just to be alive somewhere! 

 

Thanks for sharing!

Extremely well-written piece.  Above reproach for the most part, but I'm having trouble with the Law of Diminishing returns when it comes to knowledge.  There is an implication here that some knowledge will be totally beyond our reach, or there is a finite amount of knowledge in the Universe.

 

I really cannot believe these premises..

    • rekokich likes this
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llanitedave
Sep 12 2018 01:02 PM

Extremely well-written piece.  Above reproach for the most part, but I'm having trouble with the Law of Diminishing returns when it comes to knowledge.  There is an implication here that some knowledge will be totally beyond our reach, or there is a finite amount of knowledge in the Universe.

 

I really cannot believe these premises..

Well, if the universe is finite, then so is the information it contains.  However, we should still have plenty to argue about for billions of years to come.

Extremely well-written piece.  Above reproach for the most part, but I'm having trouble with the Law of Diminishing returns when it comes to knowledge.  There is an implication here that some knowledge will be totally beyond our reach, or there is a finite amount of knowledge in the Universe.

 

I really cannot believe these premises..

 

Ed,

 

I thought a great deal about the law of diminishing returns when it comes to knowledge. I define knowledge as genuine scientific and technological capability. I exclude digital data collected on our browsing history, social media experiences, and detailed shopping habits.

 

I think it is mathematically not possible for scientific capability to keep expanding at an exponential rate, because at some point it will have to double every second, then every half a second. At some point the cost of an additional increment in terms of money, time, and required infrastructure becomes too high for the expected benefit. In very general terms, we have already witnessed the phenomenon in numerous fields. It took two brothers in a bicycle shop to design the first airplane; only a couple of teenagers in a garage to make the first personal computer; only a few people with a battery, a capacitor, a coil, and a switch to make the first radio... And now it takes trillion dollar international conglomerates to make incremental improvements in the current technology. Computer CPUs seem to be approaching the upper limit of capability due to the physical limits of circuit integration and to quantum effects. We now need to stack them in order to increase capacity. And they have to be designed by artificial intelligence because no living human being has the capacity to understand what is really happening inside of them. Yes, we will develop quantum computers, but think how much more complicated and expensive that process has become.

 

With every step in knowledge and technological progress we come a step closer to some physical constant which can not be violated, or to a physical limit in measurement precision which can not be exceeded.

 

Then, there are social and financial considerations. Again, in simple terms, we are technologicaly capable of making passenger planes which fly at mach 6. We simply can't get our populations to accept constant sonic booms, and can't find a sufficient number of passengers who can afford the exorbitant price.

 

Every field of human endeavor, whether physical, intellectual, social, or economic manifests the law of diminishing returns.

 

I don't think scientific progress will ever stop, but I think it will at some point inevitably slow down to approach some undefined upper limit.

 

Rudy

    • llanitedave, jerobe and kidogofoto like this

1) Evolution is fastest when selective pressure is highest.

 

2) Dinosaurs were more intelligent than fish.  Fish are more intelligent than marine worms.  The trend towards complexity and intelligence is clear.

1) Not necessarily true and still very much under debate in the scientific community. Evolution is dependent upon mutation and selection. Mutation rates for most populations of most species are generally stable and slow, and it is the rate of mutation that determines the 'speed' of evolution, not the rate of selection. Recent research argues that certain organisms/populations under stress (what you refer to above as high selective pressure) can show increased rates of mutation. However, this trait is certainly not ubiquitous in all stressful situations or in many species, so your blanket statement does not/should not apply to the questions in the paper above.

 

2) Most definitely untrue... Evolution is not teleological. It does not have a goal or destination, certainly not intelligence (however it is defined) nor even complexity. This view is properly known as orthogenesis and the current state of evolutionary biology specifically and completely excludes anything like it.

 

Michael

    • llanitedave likes this
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llanitedave
Sep 13 2018 05:28 PM

 

2) Most definitely untrue... Evolution is not teleological. It does not have a goal or destination, certainly not intelligence (however it is defined) nor even complexity. This view is properly known as orthogenesis and the current state of evolutionary biology specifically and completely excludes anything like it.

 

Michael

For the short term, and on a smaller scale, I agree here.  But at the largest scales of time and diversity, it does seem to be a real trend.  It's not that any instance of evolution is going to result in greater complexity (whether behavioral or otherwise), but even if you look at evolution as nothing more than a random walk through some morphology or behavior space, the long-term result is that the level of complexity will increase on the high end.

 

The reason for this is a type of selection bias within the set of biological possibilities themselves.  When life originally developed it was close to, it not at, the simplest level of life possible.  There is a lower level of complexity that allows a system to be considered "living".  As far as I know, there is no upper limit that has been identified.  So it's a simple statistical fact that as species evolve and diversity increases, niches open up in more complex levels of organization.

 

As life becomes diverse enough to fill available niches, a species that evolves towards a niche of comparable or lesser complexity may find its success blocked by other species that already exist in those niches.  Niches for higher complexity, however, may be un-occupied, and a species may enter them with some possibility of success.

 

So a trend towards greater biological complexity, and with it higher intelligence, may not be an evolutionary imperative, but it does seem to be a predictable result where additional complexity is an evolutionary possibility.  We can't predict that any specific lineage will evolve in that direction, but there seems a good chance that something will.

    • Brooks Jr, rekokich and B 26354 like this


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